Like I said - people say this all the time, but a lot of vacuum tube equipment did die in EMP testing (in the USSR in 1964), and I don't see why vacuum tubes should be less vulnerable than solid state electronics to either short or long pulses (nuclear EMP contains both). A glass vacuum tube will pick up orders of magnitude more interference than a small transistor sitting inside its grounded metal can (and it's weight-prohibitive to build a metal shield around all your vacuum tubes), and the high voltage induced can damage either the vacuum tube itself, or something else inside the device. Unfortunately, very little has been published on this (although we do know that militaries test their modern solid-state devices with EMP, and they generally pass), and any online search produces a deluge of statements to the effect of "vacuum tubes are impervious to EMP" without anything to back that up. If there was ever a direct test of vacuum tubes vs. solid state, that would be very interesting to find.

People underestimate the energies produced by nuclear EMP. Car magnetos were dying in the trials, power lines and telegraph wires were getting shot through. Your nice tube amp would have no chance.